Battery and electric device

Abstract

The application provides a battery, comprising a positive electrode sheet, a negative electrode sheet and a separator in a laminated and wound arrangement. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector, and the positive electrode sheet comprises a single-coated area and a double-coated area. The positive electrode active layer is disposed on one side surface of the positive electrode sheet close to the winding center of the wound electrode body, and the positive electrode active layer of the single-coated area located in the outermost circle of the wound electrode body is provided with a functional coating on the surface away from the positive electrode current collector, and the functional coating comprises flame-retardant particles. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector, and the negative electrode active layer comprises a silicon-based material. The thickness H1 of the functional coating satisfies: 0.3 μm≤H1≤20 μm, the negative electrode active layer is provided with a plurality of grooves on the surface away from the negative electrode current collector, the width H2 of each groove satisfies: 30 μm≤H2≤250 μm, and the relationship between H1 and H2 satisfies: 2≤H2 / H1≤700.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a battery and an electrical device. Background Technology

[0002] To meet market demands, lithium-ion batteries are constantly striving for higher capacity and energy density. Based on this, silicon-based materials, with their superior theoretical specific capacity, have become a research hotspot in anode materials.

[0003] However, silicon undergoes a volume expansion of up to 280% to 300% during lithium insertion / extraction. This huge volume change leads to a decrease in the stability of the solid electrolyte interface (SEI) on the negative electrode surface. As a result, during the battery's hot box testing, the SEI film decomposes unstablely, leading to an increase in the overall heat and gas generation of the cell. This causes the battery to swell and deform, resulting in problems such as separator shrinkage, localized breakage of the positive electrode, and direct contact between the positive and negative electrodes. In particular, it increases the risk of the outermost positive electrode coating area coming into contact with the negative electrode, seriously impairing the battery's thermal and operational safety.

[0004] Therefore, while maintaining the good electrochemical performance of the battery, how to effectively improve its thermal safety performance and usage safety has become a key issue that needs to be addressed for silicon-based anode batteries to achieve large-scale commercial application. Summary of the Invention

[0005] In view of this, embodiments of this application provide a battery and electrical device to address the safety of the heat box and the safety of use in related technologies for silicon-doped negative electrode batteries.

[0006] In a first aspect, embodiments of this application provide a battery comprising a positive electrode, a negative electrode, and a separator arranged in a stacked and wound manner. The positive and negative electrode sheets are wound together with the separator to form a wound electrode body having a flat portion and a curved portion. The positive electrode includes a positive current collector and a positive active layer disposed on the positive current collector. The positive electrode includes a single-sided coating region and a double-sided coating region. The single-sided coating region is disposed near the tail end of the positive electrode and at least a portion of the single-sided coating region is located on the outermost ring of the wound electrode body. The positive active layer is disposed on the side surface of the single-sided coating region near the winding center of the wound electrode body. A functional coating, comprising flame-retardant particles, is disposed on the surface of the positive active layer of the single-sided coating region located on the outermost ring of the wound electrode body away from the positive current collector. The negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector. The negative active layer comprises a silicon-based material. The thickness H1 of the functional coating satisfies: 0.3 μm≤H1≤20 μm. Multiple grooves are provided on the surface of the negative electrode active layer away from the negative electrode current collector. The width H2 of each groove satisfies: 30 μm≤H2≤250 μm. The relationship between H1 and H2 satisfies: 2≤H2 / H1≤700.

[0007] In conjunction with the first aspect above, in one possible implementation, the thickness H1 of the functional coating satisfies: 0.5 μm ≤ H1 ≤ 10 μm, and / or, the width H2 of each groove satisfies: 50 μm ≤ H2 ≤ 200 μm; and / or, the depth H3 of each groove satisfies: 5 μm ≤ H3 ≤ 40 μm; and / or, the distance H4 between two adjacent grooves satisfies: 0.5 mm ≤ H4 ≤ 2 mm.

[0008] In conjunction with the first aspect above, in one possible implementation, the median particle size Dv50 of the flame-retardant particles satisfies: 0.01 μm ≤ Dv50 ≤ 3.0 μm.

[0009] In conjunction with the first aspect above, in one possible implementation, the particle size distribution width of the flame-retardant particles is defined as the ratio of the difference between Dv90 and Dv10 of the flame-retardant particles to Dv50 of the flame-retardant particles, and the particle size distribution width of the flame-retardant particles satisfies the following relationship: (Dv90-Dv10) / Dv50≤6; preferably, (Dv90-Dv10) / Dv50≤5.5; and / or, the relationship between the maximum particle size Dmax of the flame-retardant particles and H1 satisfies: Dmax≤0.8H1.

[0010] In conjunction with the first aspect above, in one possible implementation, the flame-retardant particles include at least one of inorganic flame-retardant materials and organic flame-retardant materials. The inorganic flame retardant materials include one or more of aluminum hydroxide, zinc borate, barium metaborate, antimony trioxide, borosilicate, aluminum phosphate, zirconium phosphate, silicon dioxide, layered silicates, magnesium oxide, magnesium hydroxide, aluminum oxide, silicon carbide, boron nitride, and aluminum titanate; the organic flame retardant materials include one or more of melamine cyanurate (MCA), melamine phosphate (MP), melamine borate (MB), and ammonium polyphosphate (APP); and / or, the functional coating further includes an adhesive, which includes one or more of polyacrylic acid, polyacrylate, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, polyolefin, fluorinated rubber, polyimide, and perfluorosulfonic acid ionomer; and / or, the functional coating further includes a conductive agent, which includes one or more of conductive carbon black (SP), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0011] In conjunction with the first aspect above, in one possible implementation, the peel strength between the functional coating of the single-sided coating area and the separator is Fc, and the peel strength between the separator and the negative electrode is Fa. Fc and Fa satisfy: Fc < Fa. Preferably, Fc and Fa satisfy: 1 ​​< Fa / Fc ≤ 8.0. Further, Fa is 8 N / m ~ 40 N / m, preferably 15 N / m ~ 35 N / m, and / or Fc is 4 N / m ~ 25 N / m, preferably 6 N / m ~ 20 N / m.

[0012] In conjunction with the first aspect described above, in one possible implementation, the single-sided coating area of ​​the positive electrode sheet has a first surface and a second surface disposed opposite to each other along the thickness direction of the positive electrode sheet. The first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center of the wound electrode body. The functional coating is located on the first surface. The first surface of the single-sided coating area of ​​the positive electrode sheet with the functional coating has a plurality of recesses, and the second surface has protrusions corresponding to the recesses.

[0013] The height D1 of each protrusion satisfies: 1 μm ≤ D1 ≤ 40 μm, the relationship between D1 and H1 satisfies: 0.08 ≤ D1 / H1 ≤ 60, preferably 0.2 ≤ D1 / H1 ≤ 40; and / or, the equivalent circle diameter S of the protrusion is defined to satisfy: 0.5 mm ≤ S ≤ 2 mm, preferably 1 mm ≤ S ≤ 2 mm, and / or, the center distance P between two adjacent protrusions satisfies: 1.2S ≤ P ≤ 4S.

[0014] In conjunction with the first aspect above, in one possible implementation, the negative electrode active layer includes a silicon-based material, wherein the mass content of silicon element in the negative electrode active layer is A wt%, and A satisfies 5≤A ≤50, and the values ​​of H1 and A satisfy the relationship: 0.01≤H1 / A≤4; preferably, 0.02≤H1 / A≤2.

[0015] In conjunction with the first aspect described above, in one possible implementation, on the outermost ring of the wound electrode body, in the curved portion, the straight-line distance between the single-sided coating area of ​​the positive electrode and the adjacent negative electrode is B1, and in the flat portion, the straight-line distance between the single-sided coating area of ​​the positive electrode and the adjacent negative electrode is B2, wherein B1 and B2 satisfy: B1 > B2; further, 0.5 μm ≤ (B1 - B2) ≤ 20 μm; preferably, 2 μm ≤ (B1 - B2) ≤ 15 μm.

[0016] Secondly, embodiments of this application provide an electrical device that includes the battery in any of the above embodiments.

[0017] According to the technical solution of this application, in the battery, the functional coating is disposed on the surface of the positive electrode active layer away from the positive electrode current collector in the single-sided coating area of ​​the positive electrode sheet. This coating provides a certain degree of isolation, reducing the risk of contact between the positive and negative electrode sheets when the separator contracts due to heat or when the battery expands, causing deformation of the positive and / or negative electrode sheets. Simultaneously, the functional coating includes flame-retardant particles, which have good thermal stability and can reduce heat transfer from the external environment to the battery interior during hot-box testing. This reduces the degree of thermal contraction of the separator or the decomposition of the SEI film under high-temperature conditions, reducing the occurrence of side reactions and the risk of contact between the positive and negative electrode sheets caused by gas expansion due to side reactions, thereby improving the battery's thermal safety.

[0018] However, after the functional coating is applied to the single-sided coating area of ​​the positive electrode, in order to avoid a large difference in compaction density between the double-sided coating area and the single-sided coating area of ​​the positive electrode, the single-sided coating area of ​​the positive electrode with the functional coating will be subjected to greater rolling stress when the electrode is rolled. At the same time, since the flame-retardant particles in the functional coating are different from the positive electrode material in the positive electrode active layer, they will undergo asynchronous deformation during rolling, further squeezing the single-sided coating area of ​​the positive electrode, which makes the positive current collector in the single-sided coating area of ​​the positive electrode prone to damage and microcracks.

[0019] Furthermore, during the rolling process of the positive electrode sheet, a sudden change in rolling stress occurs due to the thickness difference between the single-sided and double-sided coated areas. This sudden change in rolling stress at the interface between the single-sided and double-sided coated areas causes cracks in the positive electrode current collector at the interface. Adding a functional coating to the single-sided coated area increases the number of points of sudden change in rolling stress on the positive electrode sheet, thus increasing the area of ​​damage to the positive electrode current collector and raising the risk of cracks in both the single-sided coated area and the interface between the single-sided and double-sided coated areas. Moreover, because batteries containing silicon-based materials undergo significant volume changes during charging and discharging, the single-sided coated area of ​​the positive electrode sheet only has a positive active layer participating in charging and discharging on one side, resulting in more uneven expansion stress on both sides. Therefore, the damaged positive electrode current collector area is more prone to fracture under uneven expansion stress, especially at the interface between the single-sided and double-sided coated areas.

[0020] Multiple grooves are formed on the surface of the negative electrode active layer away from the negative electrode current collector. When lithium ions are embedded in the negative electrode active layer and expand, the expansion stress can be preferentially released from the grooves, allowing the negative electrode to undergo the expected and controllable deformation. Furthermore, by controlling H1 and H2 within a reasonable range and ensuring H2 / H1 is within a reasonable range, the two are matched to address both battery capacity and the issue of ineffective release of expansion stress. This reduces the lateral tensile and shear stress acting on the single-sided coating area of ​​the positive electrode sheet after battery cycling expansion, as well as at the interface between the single-sided and double-sided coating areas of the positive electrode sheet. Therefore, the risk of breakage during battery cycling can be reduced and mitigated in areas of the positive electrode single-sided coating area that are easily damaged during the rolling process after the functional coating is applied. If H2 / H1 is too small, the functional coating thickness is too thick, or the width of a single groove on the negative electrode active layer is too narrow, resulting in excessive damage to the positive electrode sheet or ineffective release of expansion stress during battery cycling, reducing the battery's cycle capacity retention rate or increasing the risk of positive electrode sheet breakage after battery cycling. When H2 / H1 is too large, the functional coating thickness is too thin or the width of a single groove on the negative electrode active layer is too wide, which makes it impossible to effectively improve the thermal safety performance of the battery, or the structural strength of the negative electrode sheet is excessively weakened, the integrity of the conductive network of the negative electrode active layer is destroyed, increasing the difficulty of lithium ion insertion into the negative electrode active layer, thereby increasing the risk of lithium plating and deteriorating the cycle performance of the battery. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a wound electrode body according to an embodiment of this application.

[0022] Figure 2 for Figure 1 Schematic diagram of the cross-sectional structure along DD.

[0023] Figure 3 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application.

[0024] Figure 4 This is a partial structural schematic diagram of a positive electrode sheet according to an embodiment of this application.

[0025] Figure 5 This is a schematic diagram of the structure of a negative electrode sheet according to an embodiment of this application.

[0026] Figure 6 This is a top view of a negative electrode sheet provided according to an embodiment of this application.

[0027] Figure 7 This is a partial structural schematic diagram of a negative electrode sheet provided according to an embodiment of this application.

[0028] Figure 8This is a partial structural schematic diagram of a wound electrode body provided according to an embodiment of this application.

[0029] Figure 9 This is a schematic diagram of a battery structure according to an embodiment of this application.

[0030] Figure 10 This is another structural schematic diagram of a battery provided according to one embodiment of this application.

[0031] Figure 11 This is a scanning electron microscope (SEM) schematic diagram of a functional coating provided according to an embodiment of this application.

[0032] Figure label: 100. Battery; 10. Wound electrode body; 101. Flat portion; 102. Bending portion; 11. Positive electrode sheet; 111. Positive electrode current collector; 112. Positive electrode active layer; 113. Single-sided coating area; 113a. First surface; 113b. Second surface; 114. Double-sided coating area; 115. Functional coating; 116. Recess; 117. Protrusion; 12. Negative electrode sheet; 121. Negative electrode current collector; 122. Negative electrode active layer; 123. Groove; 13. Separator. Detailed Implementation

[0033] The battery and electrical device according to embodiments of this application will now be described with reference to the accompanying drawings.

[0034] Exemplary battery refer to Figures 1 to 11 As shown, in a first aspect, embodiments of this application provide a battery 100, which includes a positive electrode 11, a negative electrode 12, and a separator 13 arranged in a stacked and wound manner. The positive electrode 11 and the negative electrode 12 are wound together with the separator 13 to form a wound electrode body 10 having a flat portion 101 and a curved portion 102. The positive electrode 11 includes a positive current collector 111 and a positive active layer 112 disposed on the positive current collector 111. The positive electrode 11 includes a single-sided coating region 113 and a double-sided coating region 114. The single-sided coating region 113 is disposed near the tail of the positive electrode 11, and at least a portion of the single-sided coating region 113 is located at the outermost ring of the wound electrode body 10. A positive electrode active layer 112 is disposed on the surface of the single-sided coating area 113 near the winding center of the wound electrode body 10. A functional coating 115 is disposed on the surface of the positive electrode active layer 112 of the outermost single-sided coating area 113 of the wound electrode body 10 away from the positive electrode current collector 111. The functional coating 115 includes flame-retardant particles. The negative electrode sheet 12 includes a negative electrode current collector 121 and a negative electrode active layer 122 disposed on the negative electrode current collector 121. The negative electrode active layer 122 includes a silicon-based material. Exemplarily, the silicon-based material includes at least one of silicon-carbon material and silicon-oxygen material.

[0035] The thickness H1 of the functional coating 115 satisfies: 0.3 μm≤H1≤20 μm. The surface of the negative electrode active layer 122 away from the negative electrode current collector 121 is provided with multiple grooves 123. The width H2 of each groove 123 satisfies: 30 μm≤H2≤250 μm. The relationship between H1 and H2 satisfies: 2≤H2 / H1≤700.

[0036] In one example, H1 is 0.3 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, or 20 μm, etc.

[0037] In one example, H2 is 30 μm, 40 μm, 60 μm, 90 μm, 100 μm, 120 μm, 150 μm, 180 μm, 210 μm, 240 μm or 250 μm, etc.

[0038] In one example, H2 / H1 is 2, 5, 20, 50, 80, 100, 130, 150, 200, 250, 300, 400, 500, 600, or 700, etc.

[0039] The test method for H1 in this application can be referred to in the following description.

[0040] After discharging the fully charged battery to 0% SOC, use ceramic scissors to cut along the thickness direction of the positive electrode 11. Cut the sample of the single-sided coating area 113 of the outermost ring of the positive electrode 11 of the discharged wound electrode body 10 into samples suitable for detection by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) (for example, cut the above area into 2 cm × 10 cm pieces). A 2 cm sample was used as a test sample. The cross-section of the sample was then polished using an argon ion polisher. The polished cross-section was magnified to an appropriate magnification (e.g., 1000x) using a scanning electron microscope. Energy dispersive spectroscopy (EDS) was then used to identify characteristic elements (e.g., silicon, magnesium, phosphorus, aluminum, zinc, barium, boron, etc.) of the flame-retardant particles in the functional coating 115 to distinguish the interface between the functional coating 115 and the positive electrode active layer 112. SEM was then used to randomly measure the straight-line distance between the upper surface of the functional coating 115 away from the positive electrode active layer 112 and the interface between the functional coating 115 and the positive electrode active layer 112 at multiple different locations (e.g., 10 locations) within the magnified cross-section (reference). Figure 11The thickness of the functional coating 115 can be obtained by calculating and averaging the 10 measured thickness values ​​of the functional coating 115. It can be understood that if the interface between the functional coating 115 and the positive electrode active layer 112 is uneven, the straight-line distance between the highest point of the functional coating 115 away from the positive electrode active layer 112 and the lowest point of the functional coating 115 near the positive electrode active layer 112 is used as the thickness value of the functional coating 115.

[0041] It should be noted that if the elemental composition of the flame-retardant particles in the functional coating 115 is the same as that of the positive electrode material in the positive electrode active layer 112, then by observing the particle size and packing density of the flame-retardant particles and the positive electrode active material particles in the above magnified cross-section, there will be a visible difference between the two in the above cross-section. The interface where the difference exists can be regarded as the interface between the functional coating 115 and the positive electrode active layer 112, and this interface is used as the interface for measuring the thickness of the functional layer 115. The thickness of the functional coating 115 is measured at multiple points using SEM (for example, the thickness values ​​of the functional coating 115 at 10 random locations), and the average value is calculated (the maximum and minimum values ​​can be removed and the average of the remaining values ​​is taken) to obtain the thickness H1 of the functional coating 115.

[0042] In this application, the H2 test method can be referred to in the following description.

[0043] After discharging the battery to 0% SOC, the battery was disassembled to obtain the negative electrode. The area with the groove 123 on the negative electrode 12 was cut using ceramic scissors to obtain the test sample. The test sample was then cut along a section parallel to the depth direction (Z direction) of the groove 123 and perpendicular to the length direction (X direction) of the negative electrode 12 to obtain a cross-section (e.g., ...). Figure 7 As shown, the cross-section is magnified to an appropriate magnification (e.g., 500 times) using a scanning electron microscope. Along the depth direction (Z direction) of the groove 123, multiple straight lines (e.g., 5 straight lines) are taken in sequence, connecting the left and right side walls of the groove 123 in the width direction (Y direction) and parallel to the surface of the negative electrode current collector 121. The average value of the 5 straight lines is calculated (the maximum and minimum values ​​can be removed and the average value of the remaining values ​​is taken) to obtain the width H2 of a single groove 123.

[0044] It should be noted that the length of the groove 123 is greater than its width and its depth. Furthermore, if the left and right side walls along the width direction (Y direction) of the groove 123 are uneven, then when taking the above 5 straight lines, the maximum width dimension of the left and right side walls that each straight line can connect is regarded as the width dimension of the groove 123. Then, the average value of the maximum width dimensions of the 5 straight lines can be calculated to obtain the width of a single groove 123.

[0045] In one example, the groove 123 can be formed by laser etching or machining. In another example, the groove 123 can be straight. In yet another example, the groove 123 can have an angle with the width direction of the negative electrode 12, for example, 0° to 90°.

[0046] According to the technical solution of this application, in the battery 100, the functional coating 115 is disposed on the surface of the positive active layer 112 of the single-sided coating area 113 of the positive electrode sheet 11, away from the positive current collector 111. It can play a certain degree of isolation role, reducing the risk of contact between the positive electrode sheet 11 and the negative electrode sheet 12 when the separator 13 shrinks due to heat or when the battery 100 expands and causes deformation. At the same time, the functional coating 115 includes flame-retardant particles, which have good thermal stability and can reduce the heat transfer from the outside to the inside of the battery 100 during the hot box test, thereby reducing the degree of thermal shrinkage of the separator 13, or reducing the decomposition of the SEI film of the battery 100 under high temperature environment, reducing the occurrence of side reactions, and reducing the risk of contact between the positive electrode sheet 11 and the negative electrode sheet 12 caused by gas production and swelling inside the battery 100 due to side reactions, thereby improving the thermal safety of the battery 100.

[0047] However, after the functional coating 115 is applied to the single-sided coating area of ​​the positive electrode 11, the compaction density of the double-sided coating area 114 and the single-sided coating area 113 of the positive electrode 11 differs too much. During the rolling of the electrode, the single-sided coating area 113 with the functional coating 115 will be subjected to greater rolling stress. At the same time, since the flame-retardant particles in the functional coating 115 are different from the positive electrode material in the positive electrode active layer 112, they will undergo asynchronous deformation during rolling, further compressing the single-sided coating area 113 of the positive electrode 11. This makes the positive current collector 111 in the single-sided coating area 113 of the positive electrode 11 susceptible to damage and microcracks.

[0048] Furthermore, during the rolling process of the positive electrode 11, a sudden change in rolling stress occurs due to the thickness difference between the single-sided coating area 113 and the double-sided coating area 114 of the positive electrode 11. This sudden change in rolling stress at the interface between the single-sided and double-sided coating areas 114 of the positive electrode 11 can cause cracks in the positive current collector 111 at the interface. Adding a functional coating 115 to the single-sided coating area of ​​the positive electrode increases the number of points of sudden change in rolling stress on the positive electrode 11, thereby increasing the area of ​​damage to the positive current collector 111 and increasing the risk of cracks in the single-sided coating area 113 and at the interface between the single-sided and double-sided coating areas 114 of the positive electrode 11. Then, since the battery 100 containing silicon-based materials will produce a large volume change, the positive electrode active layer 112 of the single-sided coating area 113 of the positive electrode sheet 11 only has one side participating in charging and discharging, and the expansion stress on both sides is more uneven. Therefore, the damaged positive electrode current collector 111 area is more likely to experience fatigue fracture after being subjected to uneven expansion stress.

[0049] Multiple grooves 123 are provided on the surface of the negative electrode active layer 122 away from the negative electrode current collector 121. When lithium ions are embedded in the negative electrode active layer 122 and expansion occurs, the expansion stress is preferentially released from the grooves 123, causing the negative electrode to undergo the expected and controllable deformation. Furthermore, by controlling H1 and H2 within a reasonable range and ensuring that H2 / H1 is within a reasonable range, the two are matched to address both the battery 100 capacity and the problem of ineffective release of expansion stress. This reduces the lateral tensile and shear stress acting on the single-sided coating area 113 of the positive electrode sheet 11 after the battery 100 cycles and expands, as well as on the interface between the single-sided coating area 113 and the double-sided coating area 114 of the positive electrode sheet 11. Therefore, the risk of breakage during battery 100 cycling can be reduced and mitigated in areas of the positive electrode single-sided coating area 113 that are easily damaged during the rolling process after the functional coating 115 is applied.

[0050] When H2 / H1 is too small, the functional coating 115 is too thick or the width of a single groove 123 on the negative electrode active layer 122 is too narrow, resulting in excessive damage to the positive electrode sheet 11 or the inability to effectively release the expansion stress during battery cycling, thus reducing the cycle capacity retention rate of the battery 100 or increasing the risk of breakage of the positive electrode sheet 11 after battery cycling. When H2 / H1 is too large, the functional coating 115 is too thin or the width of a single groove 123 on the negative electrode active layer 122 is too wide, resulting in the inability to effectively improve the thermal safety performance of the battery 100, or excessively weakening the structural strength of the negative electrode sheet 12, destroying the integrity of the conductive network of the negative electrode active layer 122, increasing the difficulty of lithium ion insertion into the negative electrode active layer 122, thereby increasing the risk of lithium plating and deteriorating the cycle performance of the battery 100.

[0051] In some embodiments, the thickness H1 of the functional coating 115 satisfies: 0.5 μm ≤ H1 ≤ 10 μm. For example, 0.5 μm, 0.8 μm, 1.2 μm, 1.5 μm, 4 μm, 7 μm, 9 μm, or 10 μm. Controlling the thickness of the functional coating 115 within this range can better balance heat insulation and avoid increasing the risk of damage to the positive electrode sheet 11 during the rolling process when the thickness of the functional coating 115 is set too thick, thereby increasing the risk of fracture of the positive electrode sheet 11 during the cycling of the battery 100.

[0052] In some embodiments, the thickness of the functional coating 115 is less than the thickness of the positive electrode active layer 112 to avoid reducing the volumetric energy density of the battery 100 due to ineffective thickness.

[0053] In some embodiments, the positive electrode active layer 112 includes a positive electrode material. The positive electrode material includes lithium cobalt oxide (LiCoO2), doped lithium cobalt oxide (chemical formula Li x Co 1-y1-y2-y3 A y1 B y2 C y3 O2, where 0.95 ≤ x ≤ 1.05, 0 ≤ y1 ≤ 0.1, 0 ≤ y2 ≤ 0.1, 0 ≤ y3 ≤ 0.1, and the three doping elements A, B, and C are the same or different and are independently selected from Al, Mg, Ti, Zr, Ni, Mn, Y, La, Sr, B, F), lithium iron manganese phosphate (LiFePO4) lithium iron manganese phosphate (chemical formula LiFe 1-x Mn x PO4, 0 < x < 1) and nickel cobalt manganese ternary material (chemical formula Li a Ni x Co y Mn z K b O2, where 0.85 ≤ a ≤ 1.2, 0.6 ≤ x ≤ 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2, 0 ≤ b ≤ 0.1; K is selected from at least one of Al, Ti, V, Cr, Y, W, Zr, Mg, Nb, Mo, Sr, B, and Fe); In some embodiments, the width H2 of each groove 123 satisfies: 50 μm ≤ H2 ≤ 200 μm. For example, 50 μm, 70 μm, 110 μm, 130 μm, 160 μm, 190 μm, or 200 μm. Controlling the width of the groove 123 within this range can effectively release and buffer the stress generated during the cycling of the battery 100, while avoiding damage to the structure and conductive network of the negative electrode sheet 12, thereby ensuring the cycling performance of the battery 100.

[0054] In some embodiments, the depth H3 of each groove 123 satisfies: 5 μm ≤ H3 ≤ 40 μm, for example, 5 μm, 7 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm or 40 μm. This avoids the groove 123 being too deep, which could damage the negative electrode current collector 121 body, causing the negative electrode current collector 121 to break or cause metal ions to be deposited in the negative electrode current collector 121 during battery cycling, increasing the K value of the battery 100 or deteriorating the cycle performance of the battery 100. Alternatively, if the groove 123 is too shallow, it cannot effectively store electrolyte or release stress, leading to lithium plating problems in the battery 100 or increasing the risk of the positive electrode sheet 11 breaking during battery cycling.

[0055] In this application, the depth H3 of the groove 123 can be obtained by referring to the following test method.

[0056] After discharging the battery to 0% SOC, the battery is disassembled to obtain a negative electrode sheet with a groove 123. The negative electrode sheet 12 is cut along a cross-section perpendicular to the depth direction (e.g., Z direction) and parallel to the width direction (e.g., X direction) of the groove 123 to obtain the cross-section of the groove 123 (e.g., ...). Figure 7 (As shown). Using a scanning electron microscope, the cross-section is magnified to an appropriate magnification (e.g., 500x). Along the depth direction of the groove 123 (e.g., the Z direction), the shortest straight-line distance between the bottom surface of the groove 123 closest to the negative electrode current collector and the upper surface of the negative electrode sheet that is correspondingly positioned along the depth direction of the groove 123 but does not have a groove 123 is measured. This distance is taken as the depth of the groove 123. The depths of at least five grooves 123 are measured, and then the average value is taken (the maximum and minimum values ​​can be removed, and the average of the remaining values ​​is taken) to obtain the depth H3 of the groove 123.

[0057] It should be noted that if the bottom surface of a single groove 123 or the surface of the negative electrode 12 corresponding to the single groove 123 along the depth direction of the groove 123 is an uneven surface, then when measuring the depth of the groove 123, the distance between the lowest point of the bottom surface of the groove closest to the negative current collector 121 and passing through the groove 123 and the highest point of the upper surface of the negative electrode 12 that is corresponding to the single groove 123 along the depth direction of the groove 123 and does not have a groove 123 is taken as the depth value of the groove 123. Then, the average value of the above depth values ​​is taken to obtain the depth H3 of the groove 123.

[0058] In one embodiment, the spacing H4 between two adjacent grooves 123 satisfies: 0.5 mm ≤ H4 ≤ 2 mm, for example, 0.5 mm, 0.8 mm, 1.1 mm, 1.3 mm, 1.5 mm, 1.8 mm, or 2 mm. Controlling the spacing of the grooves 123 within the above range can prevent the grooves 123 on the negative electrode active layer 122 from being too dense, which would cause excessive removal of the negative electrode active layer 122 and affect the capacity of the battery 100, or prevent the spacing of the grooves 123 from being too large, which would not effectively alleviate the local expansion stress of the battery 100.

[0059] In this application, the distance H4 between two adjacent grooves 123 can be obtained by referring to the following test method.

[0060] After discharging the battery to 0% SOC, disassemble the battery to obtain the negative electrode. Use ceramic scissors to cut the area with the groove on the negative electrode as the test sample. Cut the test sample along the length direction (e.g., Y direction) and width direction (e.g., X direction) parallel to the groove 123 to obtain the test sample (e.g., ...). Figure 6 (As shown). Using a scanning electron microscope, the surface of the sample to be tested is magnified to an appropriate magnification (e.g., 100x), and along a direction perpendicular to the width of the groove (e.g., the X direction), the shortest straight-line distance between the edges of two adjacent sides of any two adjacent uncut grooves 123 is measured (e.g., as shown). Figure 6 As shown), at least three random measurements are taken of the shortest straight-line distance between the edges of two adjacent sides of two adjacent grooves 123. The average value of the above measurements is then calculated to obtain the distance H4 between two adjacent grooves 123.

[0061] It should be noted that if any two adjacent grooves 123 have uneven sides along the width direction (e.g., the X direction) of the groove, when measuring the distance between the edges of the two adjacent sides of the two adjacent grooves, the maximum dimension of the edge that can connect the two adjacent sides of the two adjacent grooves is taken as the distance H4 between the two adjacent grooves. Then, the average value of the maximum dimension is calculated to obtain the distance H4 between the two adjacent grooves 123.

[0062] It should also be noted that the width and depth of the groove 123 on the negative electrode sheet, as well as the spacing H4 between two adjacent grooves 123, can be controlled by adjusting parameters such as the energy, frequency, and focused spot diameter of the laser, or by adjusting the distance and force between the mechanical roller and the negative electrode sheet. Specific implementation methods are not limited, as long as the corresponding structural changes can be achieved.

[0063] In one embodiment, at least one end of the groove 123 along the length direction of the negative electrode sheet 12 and / or at least one end of the groove 123 along the width direction of the negative electrode sheet 12 is a certain distance from the edge of at least one side of the negative electrode sheet 12 along the length direction and / or width direction, so as to reduce the problem of the edge of the negative electrode active layer 122 easily falling off and shedding powder during the battery 100 processing.

[0064] In another embodiment, in order to ensure the processing efficiency and consistency of the groove 123, the end of the groove 123 along the width direction of the negative electrode 12 can be flush with the edge of the width of the negative electrode 12.

[0065] In some embodiments, the functional coating 115 includes flame-retardant particles to block heat. The median particle size Dv50 of the flame-retardant particles satisfies: 0.01 μm ≤ Dv50 ≤ 3.0 μm, for example, 0.01 μm, 0.012 μm, 0.015 μm, 0.018 μm, 0.022 μm, 0.03 μm, 0.05 μm, 0.15 μm, 0.2 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 2 μm, 2.5 μm, or 3.0 μm.

[0066] By controlling the Dv50 of the flame-retardant particles within the aforementioned range, a high-quality functional coating 115 that is both dense and uniform, without sharp or hard protrusions, is formed on the positive electrode active layer 112 of the single-sided coating area 113 of the positive electrode sheet 11. This ensures efficient flame retardancy while guaranteeing the interface stability and cycle safety of the battery 100. If the median particle size Dv50 of the flame-retardant particles is too small, the particles tend to agglomerate severely, making it difficult to deagglomerate using conventional dispersion methods. This results in an uneven functional coating 115. After the battery 100 expands during cycling, the flame-retardant particles at the agglomerated locations have weak adhesion and are prone to detachment, becoming potential danger zones in the event of thermal runaway. Conversely, if the Dv50 of the flame-retardant particles is too large, the protrusion of a single large particle or a small number of particles can easily puncture the separator 13 after rolling, potentially causing a short circuit. Furthermore, excessively large particles can increase the porosity of the coating, leading to a decrease in flame-retardant performance.

[0067] More preferably, the median particle size Dv50 of the flame-retardant particles satisfies: 0.01 μm ≤ Dv50 ≤ 0.8 μm, for example, 0.01 μm, 0.02 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.4 μm, 0.6 μm, or 0.8 μm. This further ensures the density of the formed functional coating 115, thereby guaranteeing the flame-retardant effect of the functional coating.

[0068] In some embodiments, the particle size distribution width of flame-retardant particles is defined as the ratio of the difference between Dv90 and Dv10 of flame-retardant particles to Dv50 of flame-retardant particles. The Dv90, Dv10 and Dv50 of flame-retardant particles satisfy the following relationship: (Dv90-Dv10) / Dv50≤6, for example, 6, 5.5, 4.5, 4, 3.5, 3, 2.5, 1.8, 1.5, 1 or 0.5, etc.

[0069] By controlling the particle size distribution of flame-retardant particles, excessively wide particle size distribution and large particle size differences in the functional coating 115 are avoided. This leads to stress concentration points in the functional coating 115, making it difficult to flatten during rolling and easily compressing and damaging the positive electrode current collector 111. Furthermore, the different settling velocities of large and small particles in the functional coating 115 can easily cause particle stratification, reducing the particle packing density in the functional coating 115. This results in localized density and porosity issues in the functional coating 115, reducing the furnace temperature safety performance of the battery 100.

[0070] Furthermore, when (Dv90-Dv10) / Dv50 is greater than 6, the particle size distribution of the flame-retardant particles varies excessively, resulting in poor particle size uniformity. This makes the functional coating 115 prone to localized stress concentration points. After rolling the positive electrode sheet, this can easily lead to localized damage to the positive electrode current collector in the area where the functional coating 115 containing flame-retardant particles is located. Simultaneously, the poor uniformity in the size of the flame-retardant particles can also cause occasional delamination of the particles in the functional coating 115, reducing its flame-retardant or heat-insulating capabilities and thus lowering the battery's furnace temperature safety.

[0071] In one example, (Dv90-Dv10) / Dv50 ≤ 5.5, such as 5.5, 4.8, 4.6, 4.2, 3.8, 3.3, 2.8, 2.6, 2.4, 1.9, 1.7, 1.3, 0.9, or 0.4. By controlling (Dv90-Dv10) / Dv50 within the above range, a reasonable particle size distribution is achieved, ensuring the uniformity of flame-retardant particle size. This ensures the formation of a dense, uniform, and high-quality functional coating 115 on the positive electrode active layer 112 of the single-sided coating area 113 of the positive electrode sheet 11. This achieves efficient flame retardancy while ensuring the interface stability and cycle safety of the battery 100. Avoiding an excessively wide particle size distribution of flame-retardant particles, resulting in a significant number of large particles in the system, is also important. The protrusion of a single large particle or a small number of particles can easily puncture the separator 13 after rolling, causing a short circuit. At the same time, avoid excessively large particles that could increase the porosity of the coating and reduce its flame-retardant effect.

[0072] In some embodiments, the D of the flame-retardant particles V10 is 0.005 μm to 0.8 μm, for example, 0.005 μm, 0.008 μm, 0.01 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, etc., and any value in between.

[0073] In some embodiments, the D of the flame-retardant particles V 50 is 0.01 μm to 3 μm, for example, 0.01 μm, 0.012 μm, 0.015 μm, 0.02 μm, 0.03 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 2.8 μm, 3 μm, etc., and any value in between.

[0074] In some embodiments, the D of the flame-retardant particles V 90 is 0.015 μm to 5 μm, for example, 0.015 μm, 0.018 μm, 0.02 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc., and any value in between.

[0075] The maximum particle size D of the flame-retardant particles is related to H1 in the following way: D ≤ 0.8H1, for example, 0.8H1, 0.7H1, 0.6H1, 0.5H1, 0.4H1, 0.3H1, 0.2H1, or 0.1H1, so that the maximum particle size D matches the thickness of the functional coating 115. Excessive D is avoided, as a single large particle or a small number of protruding particles can easily puncture the diaphragm 13 after rolling, causing a short circuit. At the same time, excessively large particles will lead to increased coating porosity and uneven flame-retardant effect.

[0076] In this application, "median particle size" Dv50 refers to the particle size value corresponding to 50% of the cumulative volume on the cumulative distribution curve from smallest to largest volume in the volume-based particle size distribution; Dv10 refers to the particle size value corresponding to 10% of the cumulative volume on the cumulative distribution curve from smallest to largest volume in the volume-based particle size distribution; Dv90 refers to the particle size value corresponding to 90% of the cumulative volume on the cumulative distribution curve from smallest to largest volume in the volume-based particle size distribution; and the maximum particle size Dmax refers to the maximum particle diameter of the material in the volume-based particle size distribution, based on the maximum detectable particle size in the distribution curve.

[0077] In this application, the particle size of the flame-retardant particles can be tested using laser particle size analysis, specifically according to GB / T 19077-2016 "Particle Size Analysis - Laser Diffraction Method". Of course, the method for testing the particle size of flame-retardant particles is not limited to this. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) can also be used to magnify the area on the positive electrode sheet with the functional coating 115 at high magnification (e.g., magnification to 30,000x to 100,000x) to obtain a high-resolution image of the flame-retardant particles. Then, image processing software can be used to test and statistically analyze the particle size of 50 to 100 flame-retardant particles, and the Dv10, Dv50, and Dv90 of the flame-retardant particles can be calculated.

[0078] In some embodiments, the flame-retardant particles include at least one of inorganic and organic flame-retardant materials. Exemplarily, the inorganic flame-retardant material includes one or more of aluminum hydroxide, zinc borate, barium metaborate, antimony trioxide, borosilicate, aluminum phosphate, zirconium phosphate, silicon dioxide, layered silicates, magnesium oxide, magnesium hydroxide, aluminum oxide, silicon carbide, boron nitride, and aluminum titanate; the organic flame-retardant material includes one or more of melamine cyanurate (MCA), melamine phosphate (MP), melamine borate (MB), and ammonium polyphosphate (APP).

[0079] It should be noted that, in this application, "flame-retardant particles" refers to materials added to the functional coating 115 on the positive electrode 11 that can absorb heat from the surface of the burning material through endothermic decomposition, release water vapor, decompose heat molecules, and form an insoluble oxide layer to inhibit the combustion reaction and reduce the local temperature; or, by releasing non-flammable inert gases to form a heat-insulating and oxygen-barrier protective layer; or, by expanding in volume after heating to form a porous carbon layer to isolate heat and oxygen transfer; or, by absorbing gases or liquids produced by combustion through physical adsorption; or, by promoting the reaction of negative oxygen ions during combustion; or, by blocking the heat conduction path, blocking the flame and heat spread, and reducing the heat transfer rate through heat insulation, thereby inhibiting or delaying the thermal runaway reaction of the battery during furnace temperature testing by exhibiting one or more of the above-mentioned flame-retardant effects at high temperatures.

[0080] Specifically, the flame-retardant particles include at least one of inorganic flame-retardant materials and organic flame-retardant materials. The inorganic flame-retardant materials include one or more of aluminum hydroxide, zinc borate, barium metaborate, antimony trioxide, borosilicate, aluminum phosphate, zirconium phosphate, silicon dioxide, layered silicates, magnesium oxide, magnesium hydroxide, aluminum oxide, silicon carbide, boron nitride, and aluminum titanate. The organic flame-retardant materials include melamine cyanurate (MCA), melamine phosphate (MP), melamine borate (MB), and ammonium polyphosphate (APP).

[0081] In some embodiments, flame-retardant particles such as aluminum hydroxide and magnesium hydroxide can absorb a large amount of heat through decomposition reactions, thereby reducing the local temperature of the battery and achieving flame-retardant function.

[0082] In some embodiments, melamine cyanurate (MCA), melamine phosphate (MP), melamine borate (MB), and ammonium polyphosphate (APP) can expand in volume upon heating to form a porous carbon layer, which isolates heat and oxygen transfer, thereby playing a flame-retardant role.

[0083] In other embodiments, materials such as silicon carbide, boron nitride, layered silicates, and magnesium oxide can be melted or sintered at high temperatures to form a dense ceramic layer, absorbing heat and releasing water vapor to block flames and the spread of heat.

[0084] The processes and specific mechanisms by which the flame-retardant particles exert their flame-retardant effect vary, and will not be listed one by one here. It should be noted that the types of flame-retardant particles are not limited to the above-mentioned substances. Any material with the above-mentioned mechanism can be used as the flame-retardant particles in this application.

[0085] In some embodiments, the functional coating 115 further includes an adhesive to better integrate the functional coating 115 as a whole. Exemplarily, the adhesive includes one or more of polyacrylic acid, polyacrylate, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, polyolefins, fluorinated rubber, polyimide, and perfluorosulfonic acid ionomers.

[0086] In some embodiments, the functional coating 115 further includes a conductive agent to reduce internal resistance and improve cycle performance. Exemplarily, the conductive agent includes one or more of conductive carbon black (SP), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0087] It should be noted that the content of each component in the functional coating 115 is set according to the conventional settings in the field. For example, the mass ratio of flame retardant particles in the functional coating can be 5%-95%, which will not be elaborated here.

[0088] In some embodiments, the peel strength between the functional coating 115 of the single-sided coating area 113 and the separator 13 is Fc, and the peel strength between the separator 13 and the negative electrode 12 is Fa, wherein Fc and Fa satisfy: Fc < Fa. Preferably, Fc and Fa satisfy: 1 ​​< Fa / Fc ≤ 8.0, for example, 2, 3, 4, 5, 6, 7 or 8.0.

[0089] In one example, Fa is 8 N / m to 40 N / m, for example, 8 N / m, 10 N / m, 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, or 40 N / m. Preferably, Fa is 15 N / m to 35 N / m, for example, 15 N / m, 23 N / m, 26 N / m, or 33 N / m. In one example, Fc is 4 N / m to 25 N / m, for example, 4 N / m, 5 N / m, 8 N / m, 10 N / m, 15 N / m, 20 N / m, or 25 N / m. Preferably, Fc is 6 N / m to 20 N / m, for example, 6 N / m, 7 N / m, 12 N / m, 15 N / m, 18 N / m, or 20 N / m.

[0090] During the charging and discharging process of battery 100, the positive electrode material in positive electrode active layer 112 and the material in negative electrode active layer 122 will expand and contract to different degrees. The expansion of silicon-based material in negative electrode active layer 122 is more severe. Setting the peel strength Fa between separator 13 and negative electrode sheet 12 to a large value is beneficial to suppress the expansion of silicon-based material.

[0091] When Fc < Fa, when the battery 100 expands, the small adhesion between the functional coating 115 on the single-sided coating area 113 of the positive electrode 11 and the separator 13 can cause a slight slippage of this area relative to the separator 113. This avoids the risk of the functional coating 115 falling off and the reduction of the thermal safety of the battery 100 when the negative electrode expands too much, as this would cause a large shear force or extrusion force between the functional coatings 115 on the single-sided coating area 113 of the positive electrode 11.

[0092] Furthermore, during charging, the negative electrode (especially the silicon-doped negative electrode) expands, exerting a pushing force on the separator 13. The expansion stress of the negative electrode is transmitted to the separator 13, and due to the strong adhesion between the separator 13 and the negative electrode (a larger Fa), some of the stress is dissipated. Additionally, when Fc is small, the small adhesive force between the functional coating 115 of the single-sided coating area of ​​the positive electrode 11 and the separator 13 during battery expansion causes a slight relative displacement between the separator 13 and the negative electrode 12. This reduces the shear force or expansion pressure exerted on the single-sided coating area 113 of the positive electrode 11 with the functional coating 115 on the outermost edge of the battery. This reduces and mitigates the risk of breakage during battery cycling in areas of the single-sided coating area 113 of the positive electrode 11 damaged during the rolling process due to the functional coating 115. At the same time, since the profit from battery expansion is dissipated, the stress on the single-sided and double-sided interface of the positive electrode 11 can be reduced, the risk of fracture at the interface between the single-sided coating area 113 and the double-sided coating area 114 of the positive electrode 11 can be reduced, and the risk of fatigue fracture of the positive electrode 11 can be reduced.

[0093] The peel strength between the positive electrode active layer 112 and the separator 13 in the double-sided coating region 114 of the positive electrode 11 is Fc1, where Fc1 is 10 N / m to 30 N / m, for example, 10 N / m, 12 N / m, 14 N / m, 16 N / m, 18 N / m, 20 N / m, 22 N / m, 24 N / m, 26 N / m, 28 N / m, 30 N / m, or any value between them. Furthermore, Fc and Fc1 satisfy: Fc < Fc1.

[0094] Thus, the peel strength Fc between the functional coating 115 on the single-sided coating area 113 and the separator 13 is less than the peel strength Fc1 between the positive active layer 112 and the separator 13 on the double-sided coating area 114 of the positive electrode 11. On the one hand, this ensures that the ion transport path between the double-sided coating area 114 of the positive electrode 11, the separator 13, and the negative electrode 12 is as small as possible, thus maximizing the capacity of the battery 100. On the other hand, during lithium intercalation and expansion of the negative electrode, the expansion force is transmitted layer by layer. When the peel strength between the double-sided coating area 114 of the positive electrode 11 and the separator 13 is high, it can resist expansion stress, absorb some of the expansion stress transmitted inside the cell, and act as a buffer to dissipate stress. Meanwhile, the peel strength Fc between the functional coating 115 on the single-sided coating area 113 and the separator 13 is relatively low. When the remaining stress is transferred to the functional coating 115 on the single-sided coating area 113 of the positive electrode 11, where the peel strength is weakest, it can reduce the additional internal stress generated by the mechanical constraint of the separator 13 on the functional coating 115 on the single-sided coating area 113 of the positive electrode 11. Moreover, the low peel strength at this interface allows for a certain degree of controllable micro-slippage, preventing the internal stress from superimposing with the expansion stress of the battery 100 and increasing the risk of the functional coating 115 falling off. In addition, the micro-slippage between the functional coating 115 on the single-sided coating area 113 of the positive electrode 11 and the separator 13 forms a microspace. This microspace is beneficial for storing electrolyte and reduces the risk of black spot lithium plating on the negative electrode corresponding to the positive electrode single-sided coating area 113 with the functional coating 115.

[0095] refer to Figure 3 and Figure 4 In some embodiments, the single-sided coating area 113 of the positive electrode 11 has a first surface 113a and a second surface 113b disposed opposite to each other along the thickness direction of the positive electrode 11. The first surface 113a faces the winding center of the wound electrode body 10, and the second surface 113b is away from the winding center of the wound electrode body 10. The functional coating 115 is located on the first surface 113a. The first surface 113a of the single-sided coating area 113 of the positive electrode 11 with the functional coating 115 is provided with a plurality of recesses 116, and the second surface 113b is provided with protrusions 117 corresponding to the recesses 116. In this way, the expansion stress can be buffered and absorbed by the recesses 116 and the protrusions 117, thereby reducing the risk of breakage of the positive electrode 11.

[0096] In one example, the height D1 of each protrusion 117 satisfies: 1 μm ≤ D1 ≤ 40 μm, for example, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, or 40 μm. Controlling D1 within this range ensures the formation of an effective liquid storage unit of sufficient depth within the functional coating 115. Simultaneously, a stress relief zone can be formed on the positive electrode 11. When the battery 100 expands, this stress relief zone can flatten out, improving the breakage problem of the positive electrode 11 and preventing the protrusions 117 from being too small to effectively buffer and absorb stress. Furthermore, the height of the protrusions 117 is avoided from being too large, which could damage the positive current collector 111 and the structure of the flame-retardant particles in the functional coating 115, achieving a balance between the electrical performance and safety of the battery 100.

[0097] The relationship between D1 and H1 satisfies: 0.08 ≤ D1 / H1 ≤ 60, for example, 0.08, 0.1, 0.5, 1, 5, 10, 20, 30, 40, 50 or 60. Preferably, 0.2 ≤ D1 / H1 ≤ 40, for example, 0.22, 6, 12, 18, 24, 34 or 40.

[0098] In this application, the height D1 of the protrusion 117 is defined as the height of the vertex of the protrusion 117 above the first reference plane in the thickness direction of the positive electrode 11. The first reference plane is the plane containing the second surface 113b of the positive electrode 11.

[0099] By controlling D1 / H1, it is possible to avoid situations where D1 / H1 is too small, resulting in a shallow convex portion 117 or an excessively thick functional coating 115, which would severely damage the positive electrode sheet 11. If the convex portion 117 is too shallow, it cannot effectively disperse stress, limiting its effect on improving the breakage of the positive electrode sheet 11. Conversely, if D1 / H1 is too large, the convex portion 117 will be too deep, or the functional coating 115 will be too thin, potentially causing excessive damage to the structure of the functional coating 115 and the positive electrode active layer 112, reducing the thermal safety performance of the battery 100, and creating new stress concentration points at the root of the convex portion 117, increasing the risk of breakage of the positive electrode sheet 11. When D1 / H1 satisfies the above relationship, it ensures that the structure of the convex portion 117 can effectively disperse and buffer expansion stress, improving the breakage of the positive electrode sheet 11. In this case, after rolling, the convex portion 117 forms a firm anchoring point with the separator 13, while simultaneously constructing a three-dimensional "skeleton" structure within the positive electrode sheet 11. When the positive electrode 11 is subjected to stress, the frame can effectively distribute the stress over a larger area, thereby reducing the risk of breakage of the positive electrode 11.

[0100] In one example, the equivalent circular diameter S of the protrusion 117 is defined to satisfy: 0.5 mm ≤ S ≤ 2 mm, for example, 0.5 mm, 0.8 mm, 1 mm, 1.3 mm, 1.5 mm, 1.8 mm, or 2 mm. Preferably, 1 mm ≤ S ≤ 2 mm, for example, 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, or 2 mm. When the equivalent circular diameter of the protrusion 117 is within the above range, it can both allow the formation of a recess 116 on the functional coating 115 that matches the size of the protrusion 117, improving the liquid storage effect of the functional coating 115 and reducing the risk of lithium plating in the battery 100, and ensure that the equivalent circular diameter S of the protrusion 117 is not too small, which would cause excessive local compression of the functional coating 115, resulting in local peeling of the functional coating 115 or local stress concentration points in the positive electrode 11, leading to breakage of the positive electrode 11. If S is too large, the bonding stability between the separator 13 and the positive electrode 11 will decrease, increasing the risk of local lithium plating in the battery 100 and reducing the cycle performance of the battery 100.

[0101] In one example, the center distances P and S between two adjacent protrusions 117 satisfy: 1.2S≤P≤4S, for example, 1.2S, 0.5S, 2S, 2.5S, 3S or 3.5S.

[0102] In this way, the center distances P and S between two adjacent protrusions 117 satisfy the above range, which can ensure the connection stability between the concave portion 116 and the non-concave portion on the functional coating 115, prevent the functional coating 115 from falling off, and also make the protrusions 117 form a uniformly distributed macroscopic reinforcement area on the surface of the positive electrode 11. When the battery 100 expands, it can efficiently redistribute the linear stress or point stress into surface stress to avoid stress concentration that could cause the positive electrode 11 to break.

[0103] In this application, the equivalent circle diameter S of the convex portion 117 can be determined using the following test method.

[0104] After discharging the battery to 0% SOC, the battery is disassembled to obtain the positive electrode 11. A 2 cm × 2 cm positive electrode 11 with a protrusion 117 is cut along the thickness direction of the positive electrode 11. The cut positive electrode 11 is magnified to an appropriate magnification (e.g., 500x) using a scanning electron microscope to obtain a clear SEM image of the positive electrode 11 with the protrusion. Using image processing software, a measurement line is drawn along the height direction of the protrusion 117, and the height of the protrusion 117 is calculated based on the image pixel information and the known magnification. Similarly, in the SEM image, the diameter of the protrusion 117 is measured using image processing software. By randomly measuring the circumscribed circle diameters of 10 different protrusions 117, the average value is calculated (the maximum and minimum values ​​can be removed, and the average of the remaining values ​​is taken) to obtain the equivalent circular diameter S of the protrusion 117.

[0105] It should be noted that when the protrusion 117 is irregular in shape, the straight-line distance between the two farthest points of a single protrusion 117 is measured as the equivalent circle diameter S of the protrusion 117.

[0106] In this application, the method for measuring the center distance P between two adjacent protrusions 117 can be referred to the following description. After discharging the battery to 0% SOC, the battery is disassembled to obtain the positive electrode 11. A test sample of the positive electrode 11 with protrusions 117 and a diameter of 2 cm × 2 cm is cut along the thickness direction of the positive electrode 11. The test sample of the cut positive electrode 11 is magnified to an appropriate magnification (e.g., 500 times) using a scanning electron microscope. Ten to twenty (e.g., 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20) protrusions 117 are randomly selected on the surface of the test sample. The distance between the centers of two adjacent protrusions 117 among the above ten to twenty protrusions 117 is measured, and the average value is taken (the maximum and minimum values ​​can be removed and the average value of the remaining values ​​is taken), which is the center distance P between two adjacent protrusions 117.

[0107] It should be noted that when two adjacent protrusions 117 are irregularly shaped, the straight-line distance between the highest points of the two adjacent protrusions 117 is measured as the center distance P between the two adjacent protrusions 117.

[0108] In some embodiments, the negative electrode active layer 122 comprises a silicon-based material, and the mass content of silicon element in the negative electrode active layer 122 is A wt%, where A satisfies 5 ≤ ​​A ≤ 50, for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 40 wt%, or 50 wt%. The numerical values ​​of H1 and A satisfy the relationship: 0.01 ≤ H1 / A ≤ 4, for example, 0.01, 0.1, 0.5, 0.8, 1, 1.5, 2, 3, or 4. Preferably, 0.02 ≤ H1 / A ≤ 2, for example, 0.02, 0.4, 0.6, 1.2, 1.4, 1.8, or 2.

[0109] The increased silicon content exacerbates the instability of battery 100 during hot-box testing. Therefore, a sufficiently thick functional coating 115 (H1) is necessary to provide matching flame retardant and thermal stability. If H1 / A is too small, the SEI film decomposes more severely on the high-silicon-content negative electrode 12 during battery 100 cycling, leading to increased heat and gas generation in the battery 100 and causing it to swell and deform. In this case, if the corresponding functional coating 115 is too thin, it cannot effectively prevent battery 100 from catching fire, failing to enhance the battery's thermal safety during hot-box testing. This will result in a lower pass rate for battery 100 in hot-box testing. An excessively high H1 / A ratio means that the functional coating 115 is too thick relative to the silicon content. This will have several negative effects: First, the excessively thick functional coating 115 directly increases the mass and volume of the inactive material, significantly reducing the energy density of the battery 100; second, the excessively thick functional coating 115 will become a significant obstacle to the transport of lithium ions from the electrolyte to the positive electrode active material, greatly increasing the interfacial impedance and causing black spot lithium plating on the corresponding negative electrode 12; third, the excessively thick functional coating 115 will increase the sites of sudden stress changes during the rolling of the positive electrode 11, increasing the risk of damage to the positive electrode 11, and thus increasing the risk of breakage of the positive electrode 11.

[0110] It should be noted that the mass content of silicon in the negative electrode active layer 122 can be controlled by improving the mass ratio of silicon-based materials in the negative electrode active layer 122 or by changing the mass ratio of silicon in the silicon-based materials.

[0111] The method for testing the mass percentage of silicon in the negative electrode active layer 122 is described below.

[0112] A. Thermogravimetric analysis (TGA) was used for testing. The specific method is as follows: After discharging the lithium-ion secondary battery to 0% SOC, the negative electrode 12 was disassembled and removed. It was then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove the lithium salt adhering to the negative electrode 12. After drying, the negative electrode 12 was subjected to high-temperature treatment at 400℃ in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer 122 could then be peeled off from the negative electrode current collector 121, and the peeled-off negative electrode active material was collected. In the silicon content test, a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer) was used. The sample amount used for testing was 5 mg to 15 mg. Under an air or oxygen atmosphere, the temperature was increased from room temperature to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40 min. This allowed the non-silicon components in the negative electrode active layer 122 to volatilize while the silicon was fully oxidized to silicon dioxide. The weight percentage at the end of the entire test process is the ash content of silicon dioxide in the negative electrode active layer 122; the ash content is divided by the molar mass of silicon dioxide (60) and then multiplied by the molar mass of silicon (28) to obtain the percentage content of silicon in the negative electrode active layer 122.

[0113] refer to Figure 8 In some embodiments, at the outermost ring of the wound electrode body 10, in the bent portion 102, the straight-line distance between the single-sided coating area 113 of the positive electrode 11 and the adjacent negative electrode 12 is B1; in the flat portion 101, the straight-line distance between the single-sided coating area 113 of the positive electrode 11 and the adjacent negative electrode 12 is B2, where B1 and B2 satisfy: B1 > B2. In one example, 0.5 μm ≤ (B1 - B2) ≤ 20 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 5 μm, 8 μm, 10 μm, 14 μm, 16 μm, 18 μm, or 20 μm. Preferably, 2 μm ≤ (B1 - B2) ≤ 15 μm, for example, 2 μm, 4 μm, 6 μm, 9 μm, 11 μm, 12 μm, 13 μm, or 15 μm.

[0114] The stress experienced by different regions of the wound electrode body 10 is uneven. Compared to the flat portion 101, the curved portion 102 experiences greater expansion and compressive force, and the single-sided coating area 113 of the positive electrode 11 is at least partially located on the outermost ring of the wound electrode body 10. Due to the characteristics of the wound structure, the closer to the outer ring of the wound electrode body 10, the greater the expansion force it experiences from the inside out, which is accumulated layer by layer. During charging, the negative electrode 12 expands, and the distance between the electrodes decreases. Because the initial value of B1 is larger, it provides additional expansion margin for the larger radial stress on the outermost ring. This is equivalent to reducing the compressive strain rate of the separator 13 and the tensile strain rate of the positive current collector 111 in the outermost ring region, thereby reducing the stress peak. Therefore, it is ensured that the stress does not excessively concentrate on the outermost ring (the position with the greatest curvature) of the wound electrode body 10, thus improving the problem of positive electrode 11 breakage. In addition, (B1-B2) is controlled within a certain range to ensure the structural stability of the wound electrode body 10, and to avoid the structure of the wound electrode body 10 becoming loose, hindering lithium insertion and extraction, and causing a decrease in the electrical performance of the battery 100.

[0115] It is understood that, here, in the outermost ring of the wound electrode body, at the curved portion 102, the straight-line distance B1 between the single-sided coating area 113 of the positive electrode 11 and the adjacent negative electrode 12 refers to the straight-line distance between the single-sided coating area 113 and the directly adjacent negative electrode 12; in the flat portion 101, the straight-line distance B2 between the single-sided coating area 113 of the positive electrode 11 and the adjacent negative electrode 12 refers to the straight-line distance between the single-sided coating area 113 and the directly adjacent negative electrode 12. Furthermore, a separator is provided between the positive and negative electrodes. The specific meanings of B1 and B2 can refer to the sum of the gap between the single-sided coating area 113 of the positive electrode 11 and the adjacent negative electrode 12, and the thickness of the separator between the single-sided coating area 113 of the positive electrode 11 and the adjacent negative electrode 12, in the curved portion 102 and the flat portion 101 of the outermost ring of the wound electrode body.

[0116] The difference between B1 and B2 can be achieved by providing separators 13 of different thicknesses in the curved portion 102 and flat portion 101 of the outermost ring of the wound electrode body 10; or, during the winding manufacturing of the battery, plastic sheets of different thicknesses can be provided in the curved portion 102 and flat portion 101 of the outermost ring of the wound electrode body 10, and the plastic sheets can be removed after winding to change the straight-line distance between the single-sided coating area 113 of the positive electrode 11 and the negative electrode 12 in different regions of the wound electrode body 10; or, the straight-line distance between the single-sided coating area 113 of the positive electrode 11 and the negative electrode 12 can be changed at different positions by providing a positive active layer 112 of different thickness or a functional coating 115 of different thickness in the single-sided coating area 113 of the positive electrode 11 in the curved portion 102 and flat portion 101 of the outermost ring of the wound electrode body 10.

[0117] It should be noted that there are no specific restrictions on the methods used to achieve the difference in distance between B1 and B2; other methods besides those listed above that can achieve the aforementioned difference are also acceptable. The specific values ​​of B1 and B2 can be obtained by performing CT non-destructive testing on the battery.

[0118] It is understood that B1 and B2 refer to the gap between the surface of the functional coating 115 and the surface of the negative electrode active layer 122 of the negative electrode sheet 12 adjacent to the functional coating 115 in the curved portion 102 and the flat portion 101, respectively.

[0119] It should be noted that, for clarity, the entire structure of the battery 100 described above is not depicted. To achieve its necessary functions, those skilled in the art can configure other structures according to specific application scenarios, and the embodiments of this application do not impose such limitations. Similarly, for clarity, the entire preparation process and technology of the battery 100 described above is not depicted. To realize the preparation of the battery 100, those skilled in the art can select preparation engineering and processes according to specific application scenarios, and the embodiments of this application do not impose such limitations.

[0120] Understandably, reference Figure 9 and Figure 10 The battery 100 in this application can be a prismatic battery 100 or a pouch battery 100.

[0121] Exemplary electrical equipment Secondly, this application provides an electrical device that includes the aforementioned battery 100. Exemplarily, this electrical device can be a charging device or a power-consuming device. For example, the electrical device can be a pure electric vehicle, a hybrid electric vehicle, a range-extended electric vehicle, or a drone, etc.

[0122] The battery 100 provided according to the embodiments of this application has the corresponding effects of the battery 100 described above, as detailed above, and will not be repeated here.

[0123] It should be understood that the term "comprising" and its variations used in the embodiments of this application are open-ended, meaning "including but not limited to". The term "according to" means "at least partially according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "a plurality of" means "more than one", which implies covering two, three or more cases.

[0124] It should be understood that although terms such as "first" or "second" may be used in embodiments of this application to describe various elements, such as a first positive electrode active layer and a second positive electrode active layer, these elements are not defined by these terms, which are only used to distinguish one element from another.

[0125] The scope of protection of the embodiments of this application is not limited to the above embodiments. Any variations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the embodiments of this application should be included within the scope of protection of the embodiments of this application. Therefore, the scope of protection of the embodiments of this application should be determined by the scope of the claims.

[0126] The present application is described in detail below with reference to specific embodiments, which are used to understand rather than limit the present application.

[0127] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Unless otherwise specified, the processing procedures and techniques involved are conventional technical methods.

[0128] Example 1 Preparation of negative electrode sheet 12: Negative electrode active material (i.e., negative electrode active material, graphite and silicon-carbon composite material), sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black are dispersed in deionized water (or water) at a mass percentage of 58 (graphite): 35 (silicon-carbon composite material): 2.5: 1.5: 3, and mixed evenly to obtain a slurry. The prepared negative electrode slurry is uniformly coated onto copper foil, dried at 100°C, and then rolled and slit to obtain negative electrode sheet 12. The negative electrode active material is a graphite and silicon-carbon composite material. In the negative electrode active layer 122, the silicon content A is 15 wt%, and the silicon content in the silicon-carbon composite material is 43 wt%. The silicon content in the negative electrode active layer 122 is varied by controlling the proportion of silicon-carbon composite material in the negative electrode active material and the silicon content in the silicon-carbon composite material. Multiple grooves 123 are provided on the surface of the negative electrode active layer 122 away from the negative electrode current collector 121.

[0129] Preparation of positive electrode sheet 11: The positive electrode active material lithium nickel cobalt manganese oxide (NCM), the binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black are mixed in a mass percentage ratio of 97.2:1.8:1. An appropriate amount of N-methylpyrrolidone is added as a solvent, and the mixture is stirred until homogeneous, forming a uniformly dispersed electrode slurry with a solid content of 65 wt%. The prepared positive electrode slurry is uniformly coated onto aluminum foil, and then rolled and slit to form the positive electrode sheet 11. The positive electrode sheet 11 includes a single-sided coating area 113 and a double-sided coating area 114.

[0130] Then, following a conventional winding structure, a wound electrode body 10 is fabricated by forming the positive electrode 11, the negative electrode 12, and the separator 13. A functional coating 115 is provided on the surface of the positive active layer 112, located in the outermost single-sided coating area 113 of the wound electrode body 10, away from the positive current collector 111. The functional coating 115 comprises flame-retardant particles (e.g., alumina) and a binder (e.g., polyacrylic acid), wherein alumina and polyacrylic acid are mixed in a mass percentage ratio of 3:7, and water is used as the solvent.

[0131] Then, the wound electrode body 10 is housed in the casing and made into battery 100 through steps such as encapsulation, liquid injection, formation, secondary sealing, and capacity testing.

[0132] Electrolyte preparation: In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), add 35 wt% propyl propionate (a carboxylic acid ester compound) and 25 wt% propylene carbonate (a cyclic carbonate compound) as organic solvent, mixing to form a homogeneous solution. Slowly add 10 wt% lithium hexafluorophosphate (LiPF6) as the lithium salt and 8 wt% fluoroethylene carbonate. The remainder is ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 2:1 mass ratio as solvent. After stirring until homogeneous, the electrolyte is obtained. It should be noted that the amount of solvent in the electrolyte can be adjusted, for example, by adjusting the amount of ethylene carbonate (EC) and dimethyl carbonate (DMC), to change the amount of carboxylic acid ester compounds and cyclic carbonate compounds in the electrolyte. The remaining components of the electrolyte are set according to standard procedures and will not be described further here.

[0133] The functional coating 115 has a thickness H1 = 0.3 μm, a groove 123 width H2 = 31 μm, and H2 / H1 = 103. The groove 123 has a depth H3 = 5 μm, and the spacing between two adjacent grooves 123 is H4 = 0.4 mm. The flame-retardant particles in the functional coating 115 are alumina, with a particle size distribution (Dv50 = 0.05 μm), a particle size distribution (Dv90 = 0.2 μm), a particle size distribution (Dv10 = 0.012 μm), a ratio (Dv90 - Dv10) / Dv50 = 3.76, and a maximum particle size (Dmax = 0.24 μm). The peel strength between the functional coating 115 and the separator 13 in the single-sided coating area 113 is Fc = 4 N / m, and the peel strength between the separator 13 and the negative electrode 12 is Fa = 8 N / m, with Fa / Fc = 2. The height D1 of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is 12 μm, D1 / H1 = 40, the equivalent circle diameter S of the protrusion 117 is 0.5 mm, the center distance between two adjacent protrusions 117 is P = 1 mm, P / S = 2, H1 / A = 0.02. The straight-line distance B1 between the single-sided coating area 113 of the positive electrode 11 and the negative electrode 12 is 11.5 μm, the straight-line distance B2 between the single-sided coating area 113 of the positive electrode 11 and the negative electrode 12 is 11 μm, and (B1-B2) = 0.5 μm.

[0134] Example 2 This embodiment is based on Embodiment 1, except that the flame-retardant particles are made of silicon dioxide, the thickness of the functional coating 115 is H1=0.5 μm, the width of the groove 123 is H2=50 μm, and H2 / H1=100. The depth of the groove 123 is H3=7 μm, and the distance between two adjacent grooves 123 is H4=0.5 mm. The flame-retardant particles in the functional coating 115 have Dv50=0.02 μm, Dv90=0.05 μm, Dv10=0.01 μm, (Dv90-Dv10) / Dv50=2, and the maximum particle size of the flame-retardant particles is Dmax=0.08 μm. The peel strength between the functional coating 115 and the separator 13 in the single-sided coating area 113 is Fc=10 N / m, and the peel strength between the separator 13 and the negative electrode 12 is Fa=20 N / m, and Fa / Fc=2. The height of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is D1=30 μm, D1 / H1=60, and H1 / A=0.03. The straight-line distance between the single-sided coating area 113 of the positive electrode 11 and the negative electrode 12 is B1=11 μm, the straight-line distance between the single-sided coating area 113 of the positive electrode 11 and the negative electrode 12 is B2=9 μm, and (B1-B2)=2 μm.

[0135] Example 3 This embodiment is based on Embodiment 1, except that the flame-retardant particles are made of silicon dioxide, the thickness of the functional coating 115 is H1=5 μm, the width of the groove 123 is H2=120 μm, and H2 / H1=24. The depth of the groove 123 is H3=20 μm, and the distance between two adjacent grooves 123 is H4=1 mm. The flame-retardant particles in the functional coating 115 have Dv50=0.016 μm, Dv90=0.09 μm, Dv10=0.007 μm, (Dv90-Dv10) / Dv50=5.19, and the maximum particle size is Dmax=0.15 μm. The peel strength between the functional coating 115 and the separator 13 in the single-sided coating area 113 is Fc=15 N / m, and the peel strength between the separator 13 and the negative electrode 12 is Fa=25 N / m, with Fa / Fc=1.7. The height of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is D1=1 μm, D1 / H1=0.2, and H1 / A=0.33.

[0136] Example 4 This embodiment is based on Embodiment 1, except that the flame-retardant particles are melamine cyanurate + silica, the thickness of the functional coating 115 is H1 = 10 μm, the width of the groove 123 is H2 = 200 μm, H2 / H1 = 20, the depth of the groove 123 is H3 = 20 μm, and the distance between two adjacent grooves 123 is H4 = 1.5 mm. In the functional coating 115, the melamine cyanurate particles have a Dv50 of 0.6 μm, a Dv90 of 1 μm, a Dv10 of 0.15 μm, a (Dv90-Dv10) / Dv50 ratio of 1.42, and a maximum particle size Dmax of 1.5 μm; the silica particles have a Dv50 of 0.012 μm, a Dv90 of 0.025 μm, a Dv10 of 0.007 μm, a (Dv90-Dv10) / Dv50 ratio of 1.5, and a maximum particle size Dmax of 0.035 μm. The peel strength Fc between the functional coating 115 and the separator 13 in the single-sided coating area 113 is 20 N / m, and the peel strength Fa between the separator 13 and the negative electrode 12 is 30 N / m, with Fa / Fc = 1.3. The height of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is D1=40 μm, D1 / H1=4, S=1 mm, P=1.2 mm, P / S=1.2, and H1 / A=0.67.

[0137] Example 5 This embodiment is based on Embodiment 1, except that the flame-retardant particles are magnesium hydroxide, the thickness of the functional coating 115 is H1=20 μm, the width of the groove 123 is H2=250 μm, and H2 / H1=12.5. The depth of the groove 123 is H3=40 μm, and the distance between two adjacent grooves 123 is H4=2 mm. The flame-retardant particles in the functional coating 115 have Dv50=2.5 ​​μm, Dv90=4.2 μm, Dv10=0.7 μm, (Dv90-Dv10) / Dv50=1.4, and the maximum particle size of the flame-retardant particles is Dmax=4.5 μm. The peel strength between the functional coating 115 and the separator 13 in the single-sided coating area 113 is Fc=25 N / m, and the peel strength between the separator 13 and the negative electrode 12 is Fa=40 N / m, with Fa / Fc=1.6. The height of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is D1=1.6 μm, D1 / H1=0.08, S=2 mm, P=8 mm, P / S=4, and H1 / A=1.33.

[0138] Example 6 This embodiment is based on Embodiment 1, except that the flame-retardant particles are silicon dioxide, the thickness of the functional coating 115 is H1=0.35 μm, the width of the groove 123 is H2=245 μm, and H2 / H1=700. The depth of the groove 123 is H3=6 μm, and the distance between two adjacent grooves 123 is H4=2 mm. The silicon dioxide of the flame-retardant particles in the functional coating 115 has Dv50=0.012 μm, Dv90=0.025 μm, Dv10=0.007 μm, (Dv90-Dv10) / Dv50=1.5, and the maximum particle size of the flame-retardant particles is Dmax=0.035 μm. The peel strength between the functional coating 115 and the separator 13 in the single-sided coating area 113 is Fc=5 N / m, and the peel strength between the separator 13 and the negative electrode 12 is Fa=40 N / m, and Fa / Fc=8. The height of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is D1=4 μm, D1 / H1=11.8, S=1 mm, P=1.2 mm, P / S=1.2, and H1 / A=0.023.

[0139] Example 7 This embodiment is based on Embodiment 1, except that the flame-retardant particles are melamine phosphate + alumina, the thickness of the functional coating 115 is H1=15 μm, the width of the groove 123 is H2=30 μm, and H2 / H1=2. The depth of the groove 123 is H3=40 μm, and the distance between two adjacent grooves 123 is H4=2 mm. In the functional coating 115, the melamine phosphate in the flame-retardant particles has Dv50=0.8μm, Dv90=2.5 ​​μm, Dv10=0.4 μm, (Dv90-Dv10) / Dv50=2.63, and the maximum particle size Dmax=3 μm; the alumina has Dv50=1.2 μm, Dv90=2 μm, Dv10=0.2 μm, (Dv90-Dv10) / Dv50=4, and the maximum particle size Dmax=2.2 μm. The peel strength Fc between the functional coating 115 of the single-sided coating area 113 and the separator 13 is 19.5 N / m, and the peel strength Fa between the separator 13 and the negative electrode 12 is 20 N / m, with Fa / Fc = 1.03. The height D1 of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is 35 μm, D1 / H1 = 2.3, S = 1 mm, P = 1.2 mm, P / S = 1.2, and H1 / A = 1.

[0140] Example 8 This embodiment is based on Embodiment 3. The flame-retardant particles are silicon dioxide. The difference is that the flame-retardant particles in the functional coating 115 have Dv50=0.008 μm, Dv90=0.03 μm, Dv10=0.002 μm, (Dv90-Dv10) / Dv50=3.5, and the maximum particle size of the flame-retardant particles is Dmax=0.1 μm.

[0141] Example 9 This embodiment is based on Embodiment 3. The flame-retardant particles are silicon dioxide. The difference is that the flame-retardant particles in the functional coating 115 have Dv50=3.5 μm, Dv90=4.5 μm, Dv10=0.8 μm, (Dv90-Dv10) / Dv50=1.06, and the maximum particle size of the flame-retardant particles is Dmax=5 μm.

[0142] Example 10 This embodiment is based on Embodiment 3. The flame-retardant particles are silicon dioxide. The difference is that the flame-retardant particles in the functional coating 115 have Dv90=0.12 μm, Dv50=0.016 μm, Dv10=0.007 μm, (Dv90-Dv10) / Dv50=7.06, and the maximum particle size of the flame-retardant particles is Dmax=0.2 μm.

[0143] Example 11 This embodiment is based on embodiment 3, except that Fa=5 N / m and Fa / Fc=0.3.

[0144] Example 12 This embodiment is based on embodiment 3, except that Fa=50 N / m and Fa / Fc=3.3.

[0145] Example 13 This embodiment is based on embodiment 3, except that Fc = 3 N / m and Fa / Fc = 8.3.

[0146] Example 14 This embodiment is based on embodiment 3, except that Fc = 30 N / m and Fa / Fc = 1.2.

[0147] Example 15 This embodiment is based on embodiment 3, except that D1=0.5 μm and D1 / H1=0.1.

[0148] Example 16 This embodiment is based on Embodiment 3, except that D1=50 μm and D1 / H1=10.

[0149] Example 17 This embodiment is based on Embodiment 3, except that D1=0.35 μm and D1 / H1=0.07.

[0150] Example 18 This embodiment is based on Embodiment 3. The flame-retardant particles are silicon dioxide. The difference is that the thickness H1 of the functional coating is 0.5 μm, D1=50 μm, and D1 / H1=100.

[0151] Example 19 This embodiment is based on embodiment 3, except that S=0.3 mm and P=2 mm.

[0152] Example 20 This embodiment is based on embodiment 3, except that S=3 mm and P=2 mm.

[0153] Example 21 This embodiment is based on Embodiment 3, except that in the negative electrode active layer 122, the mass content of silicon element A=56wt% and H1 / A=0.09.

[0154] Example 22 This embodiment is based on Embodiment 3, except that the silicon content A in the negative electrode active layer 122 is 1wt%, and H1 / A=5.

[0155] Example 23 This embodiment is carried out with reference to Embodiment 3. The flame retardant particles are silicon dioxide. The difference is that the thickness H1 of the functional coating is 0.3 μm, the width H2 of the groove 123 is 31 μm, and the mass content of silicon element in the negative electrode active layer 122 is A=38 wt%, H1 / A=0.008.

[0156] Example 24 This embodiment is based on embodiment 3, except that B1 = 15 μm, B2 = 10 μm, and (B1-B2) = 5 μm.

[0157] Example 25 This embodiment is based on embodiment 3, except that B1 = 25 μm, B2 = 5 μm, and (B1-B2) = 20 μm.

[0158] Example 26 This embodiment is based on embodiment 3, except that B1=15 μm, B2=11 μm, and (B1-B2)=4 μm.

[0159] Example 27 This embodiment is based on embodiment 3, except that B1 = 27 μm, B2 = 5 μm, and (B1-B2) = 22 μm.

[0160] Comparative Example 1 This embodiment is based on Embodiment 3, except that H1=0.15 μm, H2 / H1=800, and D1 / H1=0.04.

[0161] Comparative Example 2 This embodiment is based on Embodiment 3, except that H1=28 μm, H2 / H1=4.3, and D1 / H1=0.04.

[0162] Comparative Example 3 This embodiment is based on Embodiment 3, except that H2=10 μm and H2 / H1=2.

[0163] Comparative Example 4 This embodiment is based on Embodiment 3, except that H2=360 μm and H2 / H1=72.

[0164] Comparative Example 5 This embodiment is based on Embodiment 3, except that H1=20 μm, H2=10 μm, H2 / H1=0.5, and D1 / H1=0.05.

[0165] Material property testing 1. H1, H2, H3, H4, D1, S, B1, and B2 were obtained by microscopy, scanning electron microscopy, or CT testing.

[0166] 2. Furnace temperature test conditions and methods (including sample quantity): 1) Sample grouping: 100 samples of 10 batteries were tested for each embodiment; 2) Test methods: The experiment was conducted at 25 ℃±5 ℃ using the following steps: a. Discharge to the lower limit voltage at 0.2C.

[0167] b. Let stand for 5 minutes.

[0168] c. Charge to the upper limit voltage at 0.7C, with a cutoff current of 0.02C.

[0169] d. Test the voltage, internal resistance, and thickness of a fully charged 100 battery at 25℃ + 5℃, and take a picture before the test.

[0170] e. Place the fully charged battery 100 in an oven and heat it at a rate of 5 ℃ / min ± 2 ℃ / min. When the temperature inside the oven reaches 130 ℃, keep it at that temperature for 10 min.

[0171] f. Continue heating using this procedure. After the oven temperature reaches 131℃ and 132℃, maintain the temperature for 10 minutes and observe the failure status of battery 100.

[0172] Experimental results: If the temperature rises to 132℃ and the battery 100 does not catch fire or explode during the 10-minute heat preservation process, it is considered to have passed the furnace temperature performance test. For example, 2P / 10T means that 2 out of 10 batteries 100 pass the test, that is, 2 out of the 10 tested batteries 100 pass the furnace temperature test as described above.

[0173] 3. Test conditions and methods for 1000T cycle performance at room temperature (including the number of samples): 1) Sample grouping: The number of samples for each embodiment is 5.

[0174] 2) Test methods: Conduct the experiment at 25℃±+5℃ using the following steps: a. Charge at a constant current rate of 2C, cut off at a rate of 0.05C, and then discharge at a constant current rate of 4C, with a voltage range of 2.0V to 4.3V. This constitutes one charge-discharge cycle.

[0175] Experimental results: After 1000 cycles, the battery capacity retention rate was calculated.

[0176] The method for calculating the capacity retention rate of a battery after 1000T cycles at room temperature is as follows: During the cycling process, the discharge capacity C1 under the first charge-discharge cycle and the discharge capacity C1000 under the 1000th charge-discharge cycle are recorded. The capacity retention rate of the battery after 1000 cycles is (C1000 / C1) × 100%. After removing the maximum and minimum values ​​from the test results of each embodiment, the average value of the remaining values ​​is taken as the test result of each embodiment.

[0177] 4. Peel strength test between electrode and diaphragm 13 (peel strength test) After discharging the battery to 0% SOC, disassemble the battery. Take the separator 13 (25 mm wide) and the corresponding electrode area (e.g., separator and negative electrode, or separator and positive electrode double-sided area, or separator and positive electrode single-sided coated area with functional coating) (25 mm wide) and heat-press them together under a certain pressure (e.g., 1 MPa) and temperature (e.g., 90 °C). Cut them into standard samples (e.g., 25 mm wide, the bonding length between separator 13 and electrode is not less than 30 mm, and the clamping area at both ends is not less than 10 mm). Perform a peel test on a universal tensile testing machine at a peel angle of 180° and a rate of 300 mm / min. Record the flat peel strength during the stable peel stage and calculate the peel strength per unit width of the sample (N / m). Peel strength = average force value / test sample width. Each sample should be tested at least 3 times and the average value should be taken.

[0178] 5. Flame retardant particle size and distribution test A laser diffraction particle size analyzer was used. The flame-retardant particles were dispersed in a suitable solvent (such as deionized water, with the addition of a dispersant) to form a uniform suspension before measurement. The instrument software automatically generated a particle size distribution report.

[0179] 6. Test on the fracture of the single-sided coating area 113 and the boundary area between the single-sided coating area 113 and the double-sided coating area 114 of the positive electrode sheet 11 of battery 100 after high temperature (45℃) 600T: 1) Sample grouping: The number of samples for each embodiment is 20.

[0180] 2) Test methods: At an environment of 45℃±5℃, after placing battery 100 in a constant temperature test chamber for 1 hour to reach a constant temperature, conduct the test according to the following steps: a) Discharge at a constant current of 0.2C to the lower limit voltage; let stand for 5 minutes, then charge at 0.5C to the upper limit voltage of 4.53V, and then charge at a constant voltage until the current drops to 0.02C. Let stand for 5 minutes, then discharge at a constant current of 0.2C to the lower limit voltage of 3V. Record this discharge capacity as the initial capacity (D0).

[0181] b) Place battery 100 in a 45℃ constant temperature chamber for stepped charging: charge at a constant current of 3C to 4.35V, then charge at a constant current of 2.5C to 4.35V, followed by constant voltage charging until the current reaches 1.8C; charge at a constant current of 1.8C to 4.4V, then charge at a constant voltage until the current reaches 1.5C; charge at a constant current of 1.5C to 4.5V, then charge at a constant voltage until the current reaches 1.2C; charge at a constant current of 1.2C to 4.58V, then charge at a constant voltage until the current reaches 0.25C. After standing for 5 minutes, disassemble lithium-ion battery 100.

[0182] Visually inspect the disassembled battery 100 to determine the breakage status of the single-sided coating area 113 of the positive electrode 11 and the boundary area between the single-sided coating area 113 and the double-sided coating area 114. For example, 18 / 20 indicates that the aforementioned breakage problem did not occur after 18 battery cycles 100.

[0183] Table 1 shows the test results.

[0184] Table 1

Claims

1. A battery, characterized in that, include: A positive electrode, a negative electrode, and a separator are stacked and wound together. The positive and negative electrode sheets are wound together with the separator to form a wound electrode body having a flat portion and a curved portion. The positive electrode includes a positive current collector and a positive active layer disposed on the positive current collector. The positive electrode includes a single-sided coating area and a double-sided coating area. The single-sided coating area is located near the tail of the positive electrode and at least a portion of the single-sided coating area is located on the outermost ring of the wound electrode body. The positive active layer is disposed on the side surface of the single-sided coating area near the winding center of the wound electrode body. A functional coating, including flame-retardant particles, is disposed on the surface of the positive active layer of the single-sided coating area on the outermost ring of the wound electrode body away from the positive current collector. The negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector. The negative active layer includes a silicon-based material. The thickness H1 of the functional coating satisfies: 0.3 μm ≤ H1 ≤ 20 μm. The surface of the negative electrode active layer away from the negative electrode current collector is provided with multiple grooves, and the width H2 of each groove satisfies: 30 μm ≤ H2 ≤ 250 μm. The relationship between H1 and H2 satisfies: 2 ≤ H2 / H1 ≤ 700.

2. The battery according to claim 1, characterized in that, The thickness H1 of the functional coating satisfies: 0.5 μm ≤ H1 ≤ 10 μm, and / or the width H2 of each groove satisfies: 50 μm ≤ H2 ≤ 200 μm; and / or The depth H3 of each groove satisfies: 5 μm ≤ H3 ≤ 40 μm; and / or The distance H4 between two adjacent grooves satisfies: 0.5 mm ≤ H4 ≤ 2 mm.

3. The battery according to claim 1, characterized in that, The median particle size Dv50 of the flame-retardant particles satisfies: 0.01 μm ≤ Dv50 ≤ 3.0 μm.

4. The battery according to claim 3, characterized in that, The particle size distribution width of flame-retardant particles is defined as the ratio of the difference between Dv90 and Dv10 of the flame-retardant particles to Dv50 of the flame-retardant particles. The particle size distribution width of the flame-retardant particles satisfies the following relationship: (Dv90-Dv10) / Dv50≤6; preferably, (Dv90-Dv10) / Dv50≤5.5; and / or The relationship between the maximum particle size Dmax of the flame-retardant particles and H1 satisfies: Dmax≤0.8H1.

5. The battery according to claim 3, characterized in that, The flame-retardant particles comprise at least one of inorganic and organic flame-retardant materials. The inorganic flame-retardant materials include one or more of aluminum hydroxide, zinc borate, barium metaborate, antimony trioxide, borosilicate, aluminum phosphate, zirconium phosphate, silicon dioxide, layered silicates, magnesium oxide, magnesium hydroxide, aluminum oxide, silicon carbide, boron nitride, and aluminum titanate. The organic flame-retardant materials include one or more of melamine cyanurate (MCA), melamine phosphate (MP), melamine borate (MB), and ammonium polyphosphate (APP); and / or... The functional coating further includes an adhesive, which comprises one or more of polyacrylic acid, polyacrylate, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, polyolefins, fluorinated rubber, polyimide, and perfluorosulfonic acid ionomers; and / or, The functional coating also includes a conductive agent, which includes one or more of conductive carbon black (SP), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

6. The battery according to claim 1, characterized in that, The peel strength between the functional coating of the single-sided coating area and the separator is Fc, and the peel strength between the separator and the negative electrode is Fa. Fc and Fa satisfy: Fc < Fa. Preferably, Fc and Fa satisfy: 1 ​​< Fa / Fc ≤ 8.

0. Further, Fa is 8 N / m to 40 N / m, preferably 15 N / m to 35 N / m, and / or Fc is 4 N / m ~ 25 N / m, preferably 6 N / m ~ 20 N / m.

7. The battery according to any one of claims 1 to 6, characterized in that, The single-sided coating area of ​​the positive electrode sheet has a first surface and a second surface that are arranged opposite to each other along the thickness direction of the positive electrode sheet. The first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center of the wound electrode body. The functional coating is located on the first surface. The first surface of the single-sided coating area of ​​the positive electrode sheet with the functional coating has a plurality of recesses, and the second surface has a protrusion corresponding to the recesses. The height D1 of each of the protrusions satisfies: 1 μm ≤ D1 ≤ 40 μm, and the relationship between D1 and H1 satisfies: 0.08 ≤ D1 / H1 ≤ 60, preferably 0.2 ≤ D1 / H1 ≤ 40; and / or, The equivalent circular diameter S of the convex portion is defined to satisfy: 0.5 mm ≤ S ≤ 2 mm, preferably 1 mm ≤ S ≤ 2 mm, and / or, The center distances P and S between two adjacent protrusions satisfy: 1.2S ≤ P ≤ 4S.

8. The battery according to any one of claims 1 to 6, characterized in that, The negative electrode active layer comprises a silicon-based material, wherein the mass content of silicon element in the negative electrode active layer is A wt%, and A satisfies 5≤A≤50. The values ​​of H1 and A satisfy the relationship: 0.01≤H1 / A≤4; preferably, 0.02≤H1 / A≤2.

9. The battery according to any one of claims 1 to 6, characterized in that, In the outermost ring of the wound electrode body, at the curved portion, the straight-line distance between the single-sided coating area of ​​the positive electrode and the adjacent negative electrode is B1; at the flat portion, the straight-line distance between the single-sided coating area of ​​the positive electrode and the adjacent negative electrode is B2, where B1 and B2 satisfy: B1 > B2; furthermore, 0.5μm≤(B1- B2)≤20μm; preferably, 2μm≤(B1- B2)≤15μm.

10. An electrical appliance, characterized in that, Includes the battery according to any one of claims 1 to 9.

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